A. Technical Field
The present invention relates generally to optical technology, and more particularly, to optical input devices.
B. Background of the Invention
Optical technology is used in many contexts, including optical input devices, such as a mouse or a trackball, an optical printer advance mechanism, and an optical scanner. In most of these devices the optical system conventionally has a single sensor for determining the position of the optical device relative to some surface. For example, in the case of an optical mouse, the mouse has one optical sensor to determine the location of the mouse on a surface. Usually the surface is a desktop or mousepad. The position of the mouse on the surface corresponds to the position of the mouse pointer on a computer screen and the motion of the mouse on the surface translates to movement of the mouse pointer on the computer screen.
The movement of an optical mouse is determined by comparing two different images captured at two different moments in time and possibly two different locations on the surface. The ability of an optical mouse to track is highly dependent on the quality of the images. If the images are good quality, the optical mouse can more easily track.
On some surfaces an optical mouse can track well. However, there are some surfaces that present problems that the single sensor is not capable of overcoming and therefore not capable of translating the mouse motion to the mouse pointer movement. There are at least four problems with using a conventional optical mouse each of which is caused by the surface not being ideal for an optical sensor. These problems are: contrast, directionality, darkness, and an electronics problem.
The contrast problem is a result of having a glossy surface. A glossy surface lacks granularity and makes it difficult for the sensor to distinguish between a first image and a second image. The first and the second images are necessary for accurate tracking.
The directionality problem is caused by a surface being too directional, for example a wood surface. A directional surface is a surface with obvious directionality, for example, stripes or lines. On a directional surface the first image and the second image can look very similar even when motion has occurred. Most prior art optical sensors use an x-y Cartesian pixel implementation. In this implementation, the directionality problem is worse when the motion is in the 45 degrees direction relative to the directionality of the surface. Having the directionality of the stripes along the x-axis or y-axis can still cause problems, but having the directionality of the surface at a 45 degree angle to the x-axis or y-axis causes the greatest problem.
The darkness problem is caused by the surface being dark. When the surface is dark, more light is needed to get a high quality image. Since it takes more power to provide more light, there is a limit as to the amount of light that can reasonably be provided, especially in wireless optical devices. For example, providing more light requires greater power output. Wireless devices have limited power output due to power source constraints. Hence wireless devices may not be able to provide more light and the surface may still be relatively dark. When a surface is dark and there is not enough light, the images can be indistinguishable. Thus, the result can be poor tracking.
The electronics problem is caused by an automatic gain control (AGC) in the electronics of the optical device. The electronics can be set to react quickly between a very light surface and a very dark surface. When the AGC is set to react very quickly it can be unstable. Therefore, the speed of the AGC is decreased to eliminate the instability. However, once the speed has been reduced, the AGC is not capable of responding to a sudden change between a light and a dark surface. Thus, the tracking capability is adversely affected.
The problems discussed above are not limited to the optical mouse. Similar problems exist for a handheld scanner that uses an optical device to capture images and determine location and movement. Also, similar problems exist in a printer advance mechanism.
Accordingly it is desirable to provide an optical device that can sense location or movement on any surface. It is also desirable to overcome the problems of contrast, directionality, darkness, and electronics AGC.